Introduces new composable animations API, still WIP! Closes #74.

Internally when setting styles you'll instead have a callback function instead of returning styles straight

animate: AnimationCallback = (data, onFinish, setTargetProps) => {
  setTargetProps({
-   style: { display: 'none' },
+   style: (prevStyles) => ({ ...prevStyles, display: 'none' }),
  });
};

As a side, also thinking about removing className from animations internally and pumping style through emotion. That would end up making styles be fully CSS instead of inline styles. Will do in another PR though as it would be a breaking change for some consumers.

TODO:

• Get default props working through a HOC
• Squash commits
• Update readme with new animations
• Regen storybook/docs
• Add more stories for reveal/conceal move
• Solve vertically/horizontally centring children inside reveal move (still needs work, will make another issue)